(i) The electron starts from rest at plate A, therefore, the initial velocity is zero. The velocity of the electron on reaching plate B is,

v=\sqrt{\frac{2 qV}{m} }=\sqrt{\frac{2(1.602\times 10^{-19} )200}{(9.1\times 10^{-31} )} }=8.38\times 10^{6}m/s

(ii) Time taken by the electron to travel from plate A to plate B can be calculated from the average velocity of the electron in transit. The average velocity is

v_{average}=\frac{Initial  velocity+ Final  velocity}{2}=\frac{0+8.38\times 10^{6} }{2}=4.19\times 10^{6}m/s

Therefore, the time taken for travel is

Time =\frac{Separation  between  the  plates}{Average   velocity}=\frac{3 \times 10^{-3} }{4.19\times 10^{6} }=0.71\times 10^{-9}s.

(iii) Kinetic energy of the electron on reaching the plate B is

Kinetic energy = q V = (1.602 × 10^{–19}) 200 = 3.2 × 10^{–17} J